Mechanical seal assemblies are used in a wide variety of applications to prevent a fluid from leaking therethrough. For example, mechanical seal assemblies are often used in centrifugal pumps which are used to transport a process fluid. A centrifugal pump typically comprises a rotating shaft with an impeller attached to one end of the shaft for pumping the process fluid. The shaft is driven by a motor either directly or indirectly through a transmission assembly such as a gearbox. As a result, the shaft extends from a motor or gearbox housing to a pump housing which encloses the impeller. The motor or gearbox typically requires lubricated bearings to support the rotating shaft. As a result, the mechanical seal assembly is used to contain lubricant inside the motor or gearbox, thereby preventing leakage into the process fluid.
The mechanical seal assembly typically comprises a rotating member which is attached to or otherwise rotates with the shaft and a stationary member which engages the rotating member to form a mechanical seal therebetween. As the shaft rotates, frictional heat is generated between the stationary and rotating members.
The frictional heat generated between the stationary and rotating mechanical seal members can become severe enough to damage other components located nearby. In certain types of pumps, for example, an inboard bearing journally supports the shaft and is typically located inside the gearbox to receive adequate lubrication. Because the impeller is cantilevered off one end of the shaft, however, it is desirable to locate the inboard bearing as close as possible to the impeller to minimize the overhung load and resulting shaft deflection. When the shaft is rotated, the heat generated by the mechanical seal assembly due to friction may be substantial and detrimental to components located in the immediate vicinity of the mechanical seal assembly. For example, the temperature at the inboard bearing may be elevated such that oil coking occurs, thereby causing premature bearing failure from lack of lubrication.
A previous mechanical seal assembly is known which attempted to address the frictional heat problem by forming a rotating member of the mechanical seal assembly out of ceramic, which is a non-heat-conducting material. While this device did reduce the amount of frictional heat reaching the inboard bearing, the amount of localized heat at the point of contact between the stationary and rotating member increased, thereby decreasing the life of the mechanical seal assembly.